This invention relates to improvements in distance ranging apparatus and, more particularly, to a distance ranging technique and apparatus, such as a graphical digitizer, which employs a microprocessor.
Systems which perform a distance ranging function are in widespread use for various purposes. The improvement of the present invention is particularly applicable to ranging systems which employ wave energy, preferably acoustic wave energy or other wave energy which is of the nature of a mechanical disturbance, in the determination of the distance between an object and a reference location by determining the transit time of the wave energy traveling between the object and the reference. One type of equipment that employs this principle is the graphical data digitizer that is conventionally used to input graphical coordinate information, or the like, to a companion system. In a graphical data digitizer wave energy is typically passed between a movable element (such as a stylus or cursor) and one or more transducers located at fixed reference locations. The transit time of the wave energy traveling between the movable element and the reference locations is used in determining the position of the movable element, typically in terms of digital coordinates. There are many types of commerically available graphical data digitizers, and these operate in a variety of ways. For example, the type of graphical data digitizer manufactured and sold by applicants' assignee, Science Accessories Corp., measures the transit time of acoustic wave energy propagating through air. Other graphical data digitizers measure the transit time of wave energy through a solid data tablet, or through wires, etc. Regardless of the transition medium employed, a necessary part of these systems is timing circuitry for timing the travel of wave energy between the movable element and one or more reference locations or positions. Typically, clock pulses are generated at a predetermined rate and circuitry is used to initiate a count of clock pulses when the wave energy is emitted from the movable element (or the reference, depending on the mode of operation) and subsequently to terminate the count when the wave energy arrives at the reference location (or the movable element). The circuitry for generating this timing (typically, in at least two coordinates) can tend to be expensive and to increase the manufacturing cost of a graphical data digitizer equipment. The cost of this circuitry can be particularly significant when attempting to manufacture a relatively low cost system, for example, a graphical data digitizer system that would be affordable by the public at large for use in conjunction with personal computers.
Another type of equipment which employs a sonic ranging principle is an automatically focusing camera.
It is an object of the present invention to provide an improved sonic ranging apparatus and method which employs a microprocessor and uses the operational cycles of the microprocessor to effect accurate and economical range determination.